LM5021: Power sequence control by SS pin

Jason Dai

Part Number: LM5021
Other Parts Discussed in Thread: LM5020

Dear E2E,

If we would like to do the power sequence control on LM5021, could we connect a open drain FET to SS pin of LM5021 to achieve it?

Floating - enable or startup converter

Pull to ground - disable converter

BR,

Jason

over 6 years ago

0 EricLee over 6 years ago

TI__Guru 59001 points

Hi
The responsible engineer is out now. We will reply by 4/12.
Regards,
EL

0 Jason Dai over 6 years ago in reply to EricLee

TI__Expert 3720 points

Eric,

Any update?

Could LM5020 ss pin act EN pin by open drain connection?

BR,

Jason

0 EricLee over 6 years ago in reply to Jason Dai

TI__Guru 59001 points

Hi
The responsible engineer is still out of office now. He will reply by 4/23.
You can connect an open drain MOSFET to the SS pin to stop switching. Preferred way is to connect the open drain MOSFET to the UVLO pin.
Regards
EL

0 Jason Dai over 6 years ago in reply to EricLee

TI__Expert 3720 points

Eric,

There are no UVLO pin on LM5021.

Any risk or anything need to pay attention about open drain FET connect SS pin to do enable/disable?

BR,

Jason

0 EricLee over 6 years ago in reply to Jason Dai

TI__Guru 59001 points

Hi
I was confused because you used both LM5020 and LM5021 in one post. Sorry.
Regards
EL

0 Garrett Roecker over 6 years ago in reply to EricLee

TI__Mastermind 21720 points

Jason,

If you are using the LM5021 there should be no issue pulling the SS pin low to stop switching.

If you are using the LM5020 please use the UVLO pin.

thanks,

Garrett

0 Jason Dai over 6 years ago in reply to Garrett Roecker

TI__Expert 3720 points

Hello Garrett,

thanks for your reply.

May i know what the main reason is about LM5020 suggest to use UVLO pin instead of SS pin?

BR,

Jason

0 Garrett Roecker over 6 years ago in reply to Jason Dai

TI__Mastermind 21720 points

Jason,

It is because the UVLO is intended to place the device ins standby mode/ shutdown mode. In these modes the current pulled by the LM5020 is going to be lower than if the SS pin is pulled low. Pulling the SS pin low will allow for faster start-up because VCC is never discharged.

Thanks,

Garrett

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LM5021: Power sequence control by SS pin